In power generation using solar energy, such as solar power generation and solar thermal power generation, a power generation output thereof is affected by conditions of sunshine of that day, and fluctuates to a large extent. For example, the power generation cannot be performed at night, and the power generation output largely decreases on rainy and cloudy days. Moreover, when the conditions of sunshine from dawn to sunset are such conditions of sunshine as “clear and then cloudy”, the power generation output largely fluctuates within that day.
In wind power generation using wind turbines, a power generation output thereof largely fluctuates due to changes in a wind direction and a wind force on that day. For example, in such a power generation facility such as a wind farm in which a plurality of wind turbines are gathered, the power generation outputs of the respective wind turbines are added to one another, whereby short-cycle fluctuations of the power generation can be smoothed; however, the fluctuations of the power generation output thereof cannot be avoided when the power generation output is viewed as a whole.
As a technology for smoothing such a fluctuating and unstable power generation output as described above, typical is a storage battery that stores electricity when surplus generated power occurs and makes up electricity when power is insufficient. Moreover, there is known a technology called compressed air energy storage (CAES) for storing surplus generated power as an air pressure converted as an alternative of electricity when such surplus generated power occurs and then reconverting the air pressure into the electricity by an air turbine generator and the like when necessary.
For example, technologies related to such smoothing, which use the technology of CAES as described above, are disclosed in JP 2012-97737 A, JP 2013-512410 A, and JP 2013-536357 A. In the conventional technologies disclosed in these documents, energy storage efficiency is enhanced by recovering heat generated in a compression step by a compressor.